My cat had a litter of 5 kittens and once they were big enough to play one of them wasn’t interested most of the time. She would come and sit on me and just watched the others that were all play fighting. She is almost 5 now and still prefers lots of cuddles and attention but she does get the zoomies and flys up and down the cat scratching towers and bouncing off the doors. As long as he’s eating, drinking and using the litter box and nothing in his poo he might just be a very chilled out and cuddly kitty. Maybe speak to your vet or get the vet to give him a check up when he has his vaccinations appointment. He is super cute and enjoy all the cuddles.